This post will be moved in a day or so and you will get a lot more information but here are my 2 cents worth. The link above gives you a lot of information as well.
For food there are some things that are a no go like fresh fruit, vegetables and meat. If you are bringing other items across that are allowed it is best to leave them in the original containers, that way they can see easily what it is and where it was manufactured.
Gas is more but the roads are nicer so that is the trade off :B :B
Make sure you take out anything that is a no no or may raise suspicion like weapons, ammo, pepper spray, hunting items, etc. Many times it is the stupid thing that we forgot that they find like a switchblade that you have had for 30 years.
When you are stopped at the border answer the question honestly and you will be fine. They may search your rig or they may not, it is not that they suspect anything it could just be the way you came across that they figure you are as good as the next person to search.
You may want to check on health insurance as well. Sometimes your policy will cover you for 30 days with no addition other times you need to either advise them or even add a rider for a small fee.
Use cash as your credit card company will more than likely rip you off if you need to use your card. I would bring some US cash and find a Canadian Bank to exchange it at. You can use US cash any place in Canada but some smaller stores may not give you as much for it.
Above all enjoy yourself!!!!