I believe it would be smarter to book a room in a hostel if the place you go to has one. I remember the pressure I had when coming to Canada in a town where the only place I could stay was a hotel where I should pay $100 per night. I chose a place to stay mostly because I had no place to stay for the next night.
But first in Canada you can easily sublet a place. For example, in student cities, as few students stay for summer term (from May to August), you can sublet their place for cheap. The "contract" is usually a piece of paper on which you write your name, you don't even have to show an ID.
For the roommates, I suppose it is the same as any country, you cannot really know in advance if there will be a good alchemy. If you visit a dirty place or if the roommates seem very unsympathetic you'd better say no, but otherwise you cannot really know how it will be. Maybe the availability of roommates (their working times), if they say hi and talk when you visit, their cleanliness, things like that could help you. Overall, there is no reason it will be a very bad experience, but maybe you expect that they party with you or they come along to visit the city.
For the landlord, you can decide on how old the place is (and if the landlord paid for revamping it), ask the roommates if there was any problem, how fast the landlord is when something is broken, and at least if they know him, if he is easy to contact.
Anyway if you have time, start looking in advance, for Canada craigslist is quite popular, and kijiji even more. Also try to get the money prepared for when you are there (I think you should be prepared to pay the first and last month when you move in). People use cash/wire transfer for that, since cheques are not that popular.