when playing TO to teams stay over

Just wondered, when Hamilton and TO play each other do the visiting teams stay in the home town the night before or do they go on game day?

Nope... they bus in the day of the game. There's no reason for these clubs to book and pay for hotel rooms for 60 players and staff to play a road game 45 minutes away. The Argos are based at UTM so make that 30 minutes away for them to IWS.

Furthermore, the Ti-Cats use WestJet but WestJet doesn't fly from Hamilton to all of the western cities. When there isn't a direct flight, the Cats will bus to Pearson and fly from there.

I'd bet there are more than a few Ti-Cats who already live in Toronto as well..

This is where TO and Hamilton have a huge advantage over other teams. If they play each other 3 or 4 times they don't pay for hotel rooms, and they may put on a bus to go to each others stadiums. Or their players are given the choice to make their own way to the stadium depending where they live. I am sure there are players on the Ticats that live closer to Rogers Centre and players on the Argos that live closer to IWS than Rogers Centre.
For games in Montreal too the teams don't really have to take hotel rooms, but I think they do. I know they take the train to Montreal but there's not a big savings on VIA Rail.

Compare that to BC which has to take hotels and air travel for all of their away games, their costs will be considerably higher.