I own a USP .45. It was my favourite gun before I owned one, and still is now that I own one.
Off the bat, I'll admit that I have never shot a FNP.
I can attest that the USP .45 is one if the best shooters that I HAVE shot. Really soft shooting. Put over 500 rounds down the pipe over a weekend and didn't even have hand fatigue.
If this were the states, from an objective point of view, the FNP holds 3 extra rounds in the mag, comes with a threaded barrel and already comes set up for mounting a RDS. Nice features and I do like the FDE aspect.
However! To date (IMHO) nothing beats the recoil reduction system. I can't describe just how remarkable it is. For me, with slightly larger than average hands, the USP feels great. I personally like the mag extensions for the base plates. People complain about the lack of universal rail, but the sure fire MR09 fixes that up no problem. Night sights can be had, the gun will last for 100 lifetimes.
It is not uncommon for USP .45s to go hundreds of thousands of rounds without a part malfunction or breakdown with proper cleaning.
Tigger on the USP is fine. It's a battle pistol, not a match gun. Keep that in mind. Part availability isn't the best, but I don't know about the FNP. There is HK Parts in the states which makes everything easier on us HK owners.
Both seem like nice guns. For Canada, I think the choice is clear. However even if this was the states I'd still go for the USP. But I am part German and biased.
Just some thoughts.