I just found this forum on renting car seats because it mentions my business in Montreal. I can vouch for most baby equipment rental companies that we only provide the best equipment for use by visiting families to our cities. Rental is always a great option for parents travelling with small children and/or babies on a short-term basis. We have a reputation to keep up which means that we only rent good quality, clean and safe equipment. Most of us are parents too, so we know how tough it can be! Renting becomes worth the money for those who don't want the hassle (you already have your hands full with everything needed for travel with small children!).
It may be true that if you rent on a long term basis, it becomes less of a bargain, and you may think that buying one is an option. Some people do that - but then where do you put it at the end of your trip - do you bring it home, give it to a charity or leave it somewhere? My company delivers, sets-up and picks up all equipment when you need it to be at your destination, leaving you more time to enjoy your visit.
If you do not wish to rent items, it's always a good idea to ask a friend or family member if you can borrow something from someone, or maybe they could pick you up something second-hand, but as someone mentioned before, you don't know where it's been.
I hope that helps you in your decision!
Montreal Mom - Mom to Emma