I'm quite sure that this is Jacques Cartier White because I've got both the white and the pink version in my garden and I think that it is a very distinctive rose. I usually recognize it everywhere.
The leaves are much smoother as with most other portlands, very pointy, the bud form in an half opened state is very characteristcally, too.
I also have Celina Dubos and it looks quite different. Right now, I don't have really siginificant pictures to compare the roses, but I will take some in the summer and post it here.

By the way, it doesn't necessarily mean that it can't be Jacques Cartier White because Martin Weingart doesn't have this rose in his catalog. If he has received the wrong budwood, he couldn't have the correct rose. This doesn't have to be a mix-up.