There wouldn't be any problems for both uses (entry to Canada from Poland and entry to US from Canada of course).

Doesn't YYZ have sterile transit yet?

Seems they do according to this recent thread (post 13):

Transit YYZ

You would only need to enter US from Canada in this case

The procedure for connecting is outlined here:

International to USA at YYZ

A slight complication might exist if you are coming from Poland into Terminal 3 and not Terminal 1.

See T3 to T1 Issues Post #7

I had presumed you are flying LO from Warsaw which comes to Terminal 1 so should be no issues there.

While Canpass/NEXUS is valid for entry to Canada from anywhere, it is not valid to enter USA from abroad (excl Canada/WHTI) and in fact the "transit" area to enter the USA may not even have a NEXUS kiosk. Hence, it can be quicker to first enter Canada and then enter the USA from the domestic Canada end.

Don't they have a NEXUS machine installed yet in transit--this has been 2 years promised according to this thread.

If no NEXUS machine in transit area, others have reported as californiadreamin': faster to go outside

See post 58 on this thread.

See also more detail on connecting and complications of checked bags etc on posts 76+ on this thread

There is a nexus machine in the transit area. When you head into the customs hall bear left, up the escalator following the American flag signs. Collect bags, and go through nexus.

Is it worth risking your nexus membership by not carrying a passport? I don't get why this comes up every now and then. Most places seem to say the nexus card, by itself, isn't valid for airline travel. Some places do say its valid for both. If you get caught without it, and the officer believes its needed, boom. you're done. No more nexus or other trusted traveler program, possibly for life.

As far as I know the airline I am flying, Lot Polish, arrives in T1 and going to the USA I am on Delta which is T3

Well that changes a lot. Connections to T3 from T1 are never sterile AFAIK and are somewhat of an inconvenience--see
http://www.flyertalk.com/forum/catha...7-hkg-yyz.html

See also reference to post 7

T3 to T1 issues


See

T1 to T3 transit

I don't get it either. IMHO, it causes way too many problems to even consider. Yes, I am tempted to occasionally bend the rules with certain things, but not with this, or any customs/immigration issue. And also, IME, US airlines, and even AC now, tends to insist on seeing a passport as ID to travel b/t US and Canada. So even forgetting about clearing C&I, you'll want it for an airline.

Why the debate continually comes up, and how people can even get through without it is beyond me.

Not to mention TSA screeners. Yes, Nexus and Cdn drivers' licenses are valid forms of ID, according to the TSA itself. But mere recognition by the TSA officers of that fact? Good luck.

I tried presenting my Nexus card recently in LIT (of all places...) just for fun, to see what would happen. The guy looks confused for a while, eventually says, "what's this"? I start to explain... he gets more confused, so I just pull out my passport instead.

Sure, I could have tried to convince him that it's a valid document, but why bother...

I may have different luck in slightly more... um... well-traveled airports :D

Speaking of ID authenticity, after one TSA agent in ATL never saw a BC DL in his life, I started to wonder how they know if a document is authentic or not if they dodn't know how such a document looks like? They just use their UV mini flashlights and magnifying glasses.

2 UA agents were discussing the passport issue the other day at YVR while I was checking in - it is now UA policy to ensure pax have passports if they present Nexus as their ID. Wouldn't be surprised if they've been stung somewhere along the line in paying immigration fees or such for pax "turned away" by either side's customs/immigration.

Well, half the time when I check in on the US side, they insist that I must check in with the machines, which don't even read Nexus cards (the little code on the bottom of the back, which looks like the same way it reads of the bottom of your passport picture page). Looks the same to me, but the machines won't read them. I've gotten this instance even at smaller stations like CVG, which until a few months ago, didn't even have passport readers on the chickens. And IME, check in agents (and those checking at the gate) at UA have aways insisted on a passport. Once, about 9 months ago, the one checking ID at the at the gate accepted my Nexus, but usually, they insist on a passport.

I've actually noticed that the TSA screeners (at least IME, in about the last year) seem to accept it no problem. EWR used to be a problem, but towards the mid-end of last year, seem to know what they are and accept them. ORD and even CVG are also where I routinely have no trouble with a Nexus card at the TSA.

They are supposed to have a book somewhere with pictures of the official ID's from all states, provinces, and other officially allowed forms of ID. I've never seen anyone use it, but I did have an TSA agent ask if he should go get it a few years ago at ORD when he didn't know what my Nexus card was. I pulled my DL out instead, since it was easier.

Wouldn't be surprised if that individual that told you of that new "policy" was making stuff up.

I don't even bother with the Nexus card with the UA folks. Had no problem with AC folks, but UA....I just use my Passport.