Will headed (driving) to Canada -- previous trips (flying) with long gu s no issues. However, next trip driving with handgun in truck. Thus the question of paper work or?? Re handgun?

My experience is it really depends on why.

I took one to a IPSC match in Canada. It was a rather drawn out process with having to prove I was invited. This was in the early 90’s, so it has changed to some extent since then.

Self defense is generally not allowed as a reason in Canada.

There are exceptions to every rule, but handguns in Canada is very difficult for noncitizens in general.

If you have access to facebook there's an excellent user group called "Driving the AlCan" They have files of firearm transit information. Handguns can be an issue. They are restricted so require pre-approval which can be lengthy.

I've only ever transited (about 14 times now) with pump shotguns or bolt rifles. Much easier.

You might consider posing your question on the Canadian Forum.

Cheers
Jim