Clearing North American Immigration/Customs

It's a VERY long time since I've done this, and I can't remember the answer (although I think I can guess); If I fly from the UK into Canada, then on to a US city, do I have to clear customs/immigration twice - once in each country, or if I "transit" the canadian airport and go straight on to my connection into the US without "entering" Canada can I simply clear immigration and customs once at my destination US city?

Thanks,

Viz.

[preiffer]

You need to do it twice.

You have to clear customs & immigration in both the US, AND Canada. Regardless of the fact that you're "in transit", both now insist that you "enter" the country officially before continuing on to your final destination.

This applies both CA-US and US-CA.

There are two things though:

1) The Canadian customs/immigration thing has become a lot more like the US - a bit more of an interrogation than it used to be, that's for sure. BUT, it's a very light form to fill out (none of the "2nd cousin's maiden name" level of detail the US insist on.)

2) You'll clear US customs IN Canada, before departure. So when you land into the US, you're already cleared so can be straight on your way.