I'm sure that others will pop in here, but...
Streets and Trips says it's a 2.5 hr drive. Expect a lot more, and hope to be pleasantly surprised with what you get.
Expect long lines at the border. Remember that it's now a "secure" border... You might need your passport to return to the USA...but I'm not sure if that's been implemented yet.
A Google search came up with this from a FT thread about insurance:
Okay, something that I really know about. If you are leaving the USA and going to Canada, you should make sure that the car that you are driving has a Canadian Inter- Provincial Insurance Card. A card from your own personal insurance company, will NOT work. The card that you need specifically lists the VIN, year and make of the car that you are driving. I have been an insurance agent in western NY (Rochester, specifically) for the past 25 years, and I know personally of several people that were stopped and their cars impounded for failure to produce the correct card. I have overnighted the cards to clients to enable them to continue their trips. It is usually not a problem, but when there is "conflict" between the officials in Canada and the US, sometimes the rules are closely enforced.
Ask the rental company for a Canadian Insurance ID card.
And this - don't know if it applies, I'm in the middle of posting this reply and can't see your profile...
One other thing I didn't see listed here, remember that CANADIANS (I think that's Canadian residents) cannot take a U.S. rental car into Canada! Sounds unlikely I know, but if you were from Vancouver, visiting Rochester, you couldn't take that Hertz car into Niagara Falls Ontario.
One exception is one-way truck rentals, which are explicitly allowed.
Those posts were from 1999 though...
Good luck. It's been a few years since I went up there...
RFTraveler. ^