I've only crossed to Canada a couple times towing a travel trailer, but I cross often towing my sailboat to regattas. To date I have never been pulled over for secondary inspection while towing. (knock/touch wood)
I agree that either the Lewiston-Queenston or Peace Bridge are basically equal as to being trailer friendly.
Some things I believe.
Remove your sunglasses at the booth.
Open your passports/documents to the proper page before handing them over. That shows a bit of respect.
Answer the questions, but don't get too chatty. Less is more when interacting.
Once to the booth stop at the proper marked distance from the vehicle ahead. DO NOT PROCEED UNTIL THE VEHICLE AHEAD IS OBVIOUSLY AWAY OR YOU SEE A SIGNAL TO DO SO. It really p*sses them off if you pull up too soon.
Remember when entering Canada only one case of beer or one bottle of liquor per adult is allowed. (If they inspect and find partial open bottles of liquor in your trailer remember the term "bar stock". I don't know if it directly applies to travel trailers or trailered boats, but they recognize and accept that term for boats in the water. If it doesn't work at least you can say, "Sorry. I thought that it applied to my home on wheels.")
Declare long guns. You will automatically be sent to secondary to complete the proper paperwork. Canada gun laws are very strict. No handguns allowed for foreigners.
When returning to the USA keep in mind that the interaction at the booth is a "verbal declaration". If you are pulled over for a secondary inspection one of the first things that they may do is have you complete a form. That is the official document. Include everything you can remember on that document, like that extra bottle(s) of duty free liquor you forgot to mention.
Don't worry about the crossings. I cross the border often. I've had no problems when doing so in either direction.
Have fun. vic
Added: Be careful with what is on your computers. A Canadian friend of mine imported a boat from Michigan to Toronto. He fudged the selling price on the import paperwork. They did a secondary inspection and found documentation on his laptop which showed the correct selling price. Needless to say he now gets pulled over each time he returns to Canada.
You may technically have legal rights and recourse, but it is best to assume that you have no rights when entering a foreign country or even returning home to the USA . They can and will search anything they feel appropriate.