I'll be renting a car in Buffalo, NY, in July and plan to drive into Canada. While the best weekly rates can be found online, I am worried that when I show up at the rental desk in Buffalo, I'll be told I can't take the car across the border (at least at the rate I paid, or they will pressure me into buying a costly insurance waiver).
Priceline offers no guarantees on this. It says only "ask the rental agent when you check in about policy regarding travel into Canada."
Does anyone have any experience with this?
Thanks.

I have driven rental cars from Seattle, Kalispell, and Denver into Canada. Never had any questions raised. You are supposed to have an insurance yellow card to prove that you have liability insurance to cover what you do to someone else.
You might want to check with your insurance agent to make sure your policy is effective in Canada.
The collision damage waiver is supposed to be included in your credit card coverage, if you use the credit card to pay for the rental. You might also verify that you have that kind of coverage with your credit card.
I have also driven Canadian rentals into the USA with no trouble, except from an overly zealous border patrol agent who for some reason gave me the 3rd degree when I crossed into the US driving a Canadian car. (What is an American doing driving a Canadian car?? Whose car is it? and so on) Fortunately I had my passport and the rental contract close at hand.

If you are not a Canadian you should have no problem taking a US rental car into Canada. The only issue that I am aware of is for Canadians taking a US rental car into Canada. Any car driven in Canada must have liability insurance. This is not true of some US states and I don't know about NY. So check that liability is included and if not get it. Your own insurance might cover it.

Thank you for the head's up. I will contact my insurance company to make sure I'm covered. I have a proof of insurance card, but am not sure it's the right thing for driving in a foreign country.
Many thanks!

My insurance company issues me a specific yellow colored card that is required by Canadian law. I never had to show it, but I usually get it.
I forgot once and just took the whole policy with me. But check with your agent about coverage. Better safe than sorry.

We are taking a rental from Las Vegas to Vancouver. I had a hard time finding one that would let me do a one-way, but Avis did.

I looked at one of the Canadian website and learned that we needed an International drivers license and that 'yellow' card. Check AAA for the license.

Also, get some paper from your hospitalization, just to be safe.