Is customs done at port of entry or destination?
 

My parents are coming traveling from London to Toronto to Winnipeg. Let me know they'd have to clear customs at Toronto or Winnipeg.

Toronto...

You clear customs at the first airport in the new country.

ECEPTION: some countries have preclearance for customs at foreign airports. e.g. if you fly London-Toronto-New York LaGuardia, you clear US Customs right after you clear Canadian customs in Toronto since US Customs has preclearance in Toronto.

But coming into Canada? You always clear at your first Canadian airport.

Works the same way in reverse, too. Toronto-London-Edinburgh? Clear in London.

Actually, it might be (or a more definitive is) immigration and customs for carryons at the port of entry and customs for checked bags at the final stop.

yeah..this makes more sense. Thanks!!

Correct.

You clear immigration in London, you clear customs in Edinburgh.

In Canada, you clear both at port of entry.

This is true for Canada and the US, but untrue for most other countries, including the UK. Your post could be read as suggesting that there is a general rule for the "new country" but there is not.

Is the US the only country that makes you clear immigration before actually flying onto their soil? (I'm thinking about the pre-clearance areas in Canada)

No, there is no requirement by the U.S. to preclear (smaller airports on Canada, YYJ and YLW in my locality don't have them). It does make life easier for travellers who have access to pre-clearance as there's no potential for immigration/customs-caused delays when arriving into the U.S. as well as the ability to fly into airports and terminals that don't have actual immigration/customs facilities (but are still international ports of entry or customs rights designated).

Having pre-clearance is almost like MFN (most favored nation) status. The U.K. was offered that but BAA didn't want to dedicate a large area to pre-clearance not to mention losing "duty-free" sales. AFAIK, only Ireland has preclearance outside the western hemisphere.

Is customs done at port of entry or destination?
 

Abu Dhabi has US preclearance as well.

I'm not aware of any other country other than the USA that has true pre-clearance on foreign soil, however one might argue Europe has a version of this. When I flew YUL -> GVA -> BCN I cleared "European Immigration" at Geneva and did not do so again in Barcelona (I didn't leave GVA). So in effect I had cleared immigration for Spain before flying onto their soil.

I cleared customs in Spain.

Not any longer. U.S. Border Extends to Dubai to Cut Passport-Check Wait.
--
13F

I flew ZRH-LCY-GLA in '07 (maybe things have changed since then). I cleared both customs and immigration at LCY. We just picked up our bags on the carousel and departed when we arrived at GLA.

Perhaps it's done differently at LGW and LHR - LCY isn't a really major international airport. (Proof I'm a flying geek though; who would choose to internationally connect through LCY other than a flying geek?)

Schengen area. Almost all EU countries (UK excepted) plus Switzerland and Liechtenstein are in the Schengen area. You clear customs and immigration entering the Schengen area in general, and are free to travel to other Schengen countries once you're in.

It's different. I rather like it.

I cleared immigration in Switzerland - I didn't clear customs until Spain.