I think it is pretty hard to generalize, and you have to take it on a case-by-case basis. In my experience, the quality of the vinyl used in Canada in the '70s was probably higher than that of the U.S. But, if the album was first mastered in the States, the copies made in Canada were probably made from a later generation copy, and mastered differently. Sometimes, the benefit of the (different) mastering outweighs whatever negative might exist from using a later generation tape for the master. In pop records, some mastered by TLC sounded good (I've have to go back and search for titles); the first three Zep albums had some versions on the early Red Label inscribed with the letters TG which are outstanding- compared even to the "gold standard" UK plums and US RL (for LZ II). In some cases, like Columbia, for pop, the US records tend to be very bright, e.g. Blood Sweat and Tears second album, and the Canadian and UK pressings are less strident.
I'm not partial to Japanese pressings, despite the quality of the vinyl, because the EQ tends to be brighter, but again, depending on the record, there are winners. Somebody turned me on to a Japanese third pressing of LZ1, and it is outstanding, even by comparison to the UK plum with first matrices, the vaunted Piros remaster from the mid-70s and all the other uber copies I've heard or own. Of course, this is trying to make a pretty bad recording sound better, so perhaps it is not a good benchmark. I think for every rule of thumb there are exceptions. Which is why trying to get the best sounding copy often means buying a bunch of copies and doing the comparisons yourself. Obviously, a time and money-consuming exercise, particularly if you don't then sell off the copies you've decided aren't the 'best' -whatever that means. I also think in some cases, the 'differences' are a matter of sonic preference and system bias--I'm not talking about grossly bad records, but those in the zone of different shadings or points of emphasis.
