We are driving to Canada from USA the first part of August this year and our daughters passport expires the end of August. I know for travel by plane and boat to some countries, you need to have a least 6 months left on your passport. Is that true to travel by auto to and from Canada?
My understanding is that the 6 month rule applies, like you said, when boarding boats and planes. I always thought that a rule of the boat or plane company. Sometimes you can also be required a passport with an expiration of 6 months or more into the future when getting a visa.
Well, you are not getting on a boat or plane, and Canada does not require a visa to enter.
So it would seem you are ok.
Even if your passport were to expire while you or your daughter were in Canada, you could go over to the nearest US embassy in Canada and get a new passport after your passport's expiration. I'd caution you that it's a lot more hassle and more expensive to get a passport at a US embassy than it is in the US, but it is doable.
Also, I've seen CBP agents let Americans with expired passport pass through the land border with Mexico. The particular situation I saw is that a kid of a family travelling together had an expired passport, so rather than make everyone stay in Mexico, they allowed the whole family through. The parents of the kid alleged they didnt know the kid's passport had expired, and produced a birth certificate as well. So even coming back with an expired passport is a possibility, although I would highly advise against it.