Hey ANesh, very excited for you and the g/f, this is going to be an epic roady! I've done this trip 3.5 times (the .5 was cuz i flew out to pick up a truck in armstrong, bc, and drove it home), once solo, 2nd time with wife and 6 month old, and 3rd to the rockies with just my Dad. Actually jealous cuz i wont have an opportunity to go with just my wife now that we have 3 kids (for a while at least)! Anyway, sounds like we have similar travelling styles so i'll just add some tips from my experiences.
first off, a lot of the people i've met have done the trip going through canada one way and then the usa the other. might be a cool option so you can see different things and save time on the way back. i've gone through the same way you've described andc rossed back to idaho from calgary on the way back and cut across hwy 2 in the USA all the way to sioux st. marie. you can then head south to espanola past sudbury and hop on the ferry to tobermory from manitoulin island for a nice relaxing last leg of your journey back to the GTA. maybe even camp at cypress national parka and check out the Grotto/cliff jumping on georgian bay.
anyway, going there, leaving ontario is 1/3rd of the trip and there's lots to see especially up on hwy 17 along one my favourite roads around lake superior provincial park. tonnes of good camping there and lots of things to see, big rapids, waterfalls, wildlife. there's a cool beach there in Old woman cove, very quiet, good place to have a picnic or spend the night in one of the campsites. if you guys are flexible, you can just pick where you want to sleep/camp depending on how much driving you want to do on each day. i always use a road atlas (small gps or smart phone just doesn't do it justice for me) as it gives you a nice birds eye view of where you're heading and it shows all the provinicial/national parks where you can camp (and you can camp after office hours and just pay the next day/self check in) i found some cool parks this way like Obatanga waaay up north. you'll see a few on hwy 17, give any a try. as for other camping options, you can also fidn all the KOA places (a little more expensive but i use them as back up, the private places are hit and miss, so best bet for me is to stay at provincial/national parks with standard ammenities across the country for the most part)
across the praries will be quick and it also helps that you gain time westbound (but sloooow going back home as you lose the hours, lol). good place to camp in Saskatchewan is cypress hill provincial park (not too many camping spots along the praries, have to look hard, or stay at a motel depending on your timing. but you can easily do manitoba, saskatchewan and into the rockies in one day).
imho, the big highlights for such a trip is definitely the rockies and the rest of the west coast. do spend a few days in banff (and there's camping everywhere, I think Ron meant expensive if u fall foe yhe tourist traps and stay at the expensive hotels.t) and check out lake louise (do the walk around to the other end), lake morraine, emerald lake, and all the hikes in the area (kinda like niagara falls, vegas, or yellowstone, where you have to see it once at least). from there, i highly suggest taking the drive up 93/columbia ice fields parkway and checking out the columbia icefields. lots of camping along the way, so just pick and choose. HIGHLY suggest you drive up to jasper on 93 and camp/hike/site see there. most will say that jasper is nicer than banff which is more touristy, but i say do both and see for yourself. i'll never forget the hike i did with my 6 month old on my back carrier on teh Valley of 5 lakes, in Jasper (check it out, 4 hour loop and totally worth it!). anyway, you will have a smile on your face guaranteed along hwy 93 up to jasper, breathtaking views/mountains, and you might see grizzly, bobcats, elk, etc. along the way.
on to BC, you have a choice of coquihalla hwy or the crows nest pass hwy 3 (you mentioend) hwy 3 is slower and more windy but scenic, but the coquihalla is nice too and much faster, depends on your time. spend time in kelowna/okanagan for sure, pretty drive along wineries/fruit farms and it's one huge lake.
once in vancouver, you should try the grouse grind (hike up grouse mountain), it's kinda like a right of passage to vancouver if you're visiting. about a 3 hour hike and the tram down is free, treat yourself when you get to the top.
also highly suggest going up the sea to sky highway up to squamish and then whistler, ocean on one side, mountains on the other, awesome road especially on motorcycle!
if you're on the cheap, there are great hostels to stay in the vancouver area (you can get a private room for like 40 bucks or so).
now, you said Toronto to Vancouver....are you not checking out the island?! if so, you are going to miss one awesome experience. if you're out there, you might as well hop on the ferry to victoria and drive all the way to tofino (not that far) and check out the HUUGE trees in port alberni. this is a very pretty drive done in half a day and youc an camp out in tofino and hang with the surfer dudes (if you didn't know, it's a huge surfing town with some interesting peeps, some live on the beach under piles of driftwood). good camping there and a nice end destination to dip your feet in the pacific. i could also suggest taking a bush plane ride along the coast from tofino, but here's a secret, don't pay for the "whale watching tour"...ask if you can piggy back on a flight to take locals to remote reserves in some islands and pay their fare, just don't get off the plane (we saw one town there, population... 50 with 13 kids, lol), pay what the locals pay. tofino is expensive but doabl to camp and spend the night or two. also suggest checking out the pacific rim national park reserve, it's on the way. i would love to spend more time here and hike parts of it.