Well to make it simple... you have 1 potential problem and 1 guaranteed one (granted you get past the 1st problem).
First, with a criminal record you may or may not be able to visit. It's really up to the CBSA officer when you get there. You may be "criminally inadmissible" under Canadian law. You can read this site for more info but there's nothing certain saying you are or aren't allowed unless you served more than 10 years of jail time, then in that case you can't for sure. This is an official government website for Canada so anything else you read online or on forums may be out-dated or incorrect.
Second, what your gf wants to do regarding importing fruit (even frozen) into the U.S. has nothing to do with Canadian law but U.S. customs and every item must be declared to them. You can check which fruit are allowed to enter here: https://help.cbp.gov/app/answers/det...r-personal-use
You could lie and say you have nothing to declare which works sometimes but if you have a record chances are they'll be more suspicious and search your car. GL with your trip, and yea the falls view is better from the Ontario side. Also drop the superiority attitude, it won't do you any good in Canada or any country you go to... don't give them a bad impression of Americans (if you even are American...)