All good and accurate information so far. Since I travel in and out of YYZ frequently, I'll add my 3 cents.

Going in thru Canadian Customs I've learned to always check "business". I do have legit reasons for being up there frequently for work as we have a regional office there, but even on trips to see friends it results in a faster conversation. I give them my declaration card, boarding pass, business card and passport to expedite the process. The agents are fairly humorless, but they are far better at YYZ then they are at the Niagara Falls border.

Leaving from YYZ thru US Customs is pretty straight-forward. Again, any discussion of "reason" is limited to strictly business. The US agents there tend to be decent folks. Even had one share his I-phone backstage photos at a recent KISS concert. I much prefer clearing in Canada so I can just walk off the plane in the US.