Dot # For 1 Run to Pick up a Trailer?

Eventually... maybe. But it isn't in the stream of commerce now. The trailer must be inspected and approved by his home province before he can use it and, most importantly, he is not and does not engage in commerce in the US.

When I bought my truck in the US all I needed was insurance and two "in transit" permits; one for the US and one for Canada. No DOT #, nor anything else.

 

Either way, I would suggest op call customs right now anyway. I doubt it would be a problem to move the trailer, but with the border only open for essential traffic, it would blow to not be able to take it across.

 

Customs has nothing to do with it, the whole intent is to move a personal trailer to his place of business, now as soon as he puts a permanent plate on it changes.

 

He is crossing the border, so customs will at least be involved. Even when I drive my car across the border I have to talk to customs. Or whatever the official title is for the guys that check passports and asks all the questions and can deny entry.
I know right now I cannot enter Canada. Of course I'm not a Canadian like the op is.
Like I said though, it's unlikely to be an issue. It is a good idea to verify, after all it's a single phone call.

 

Customs ever ask for your operating authority, or registration?

 

You are refusing to hear what I'm saying, so after this last try I give up.
You claim it's a non commercial move.
Canada has closed the border to nonessential traffic.

Those two things together means there is a possibility that Canada will not allow the move as it may not deem it as essential. After all it's not commercial, therefore Canada might, and I emphasize might, not allow the move. It really depends on what Canada considers essential. A phone call is a lot easier to deal with than an empty trailer stuck at the border.
Unless you have something that defines that moving personal property across the border is essential.
Normally I would not have even mentioned it, but with coronavirus restrictions I dunno.

P.S. I have been asked while pulling my camper (Port Huron to Niagara Falls shortcut) if I was getting paid to move it.

 

No you aren't listening, the topic is does he need a DOT#, the answer is no, has nothing to do with customs or importing a his trailer, or border restrictions. whole different subjects.