GC44

If all goes to plan we will be flying from the UK to Winnipeg via the US. Will we need an ESTA or any other visa to transit through. We will not be staying over, just waiting for a connecting flight.

Almost Canadian

Yep

Steve_

Yes, if you're using the VWP. You need ESTA even for entries to the US from Canada by air, although as far as I'm aware Canadian airlines haven't signed up for it. There is no exemption for connecting flights through the US.

Bob

It's only land borders where you don't need ESTA.

Makes a connecting flight not so fun.

G77

Won't the OP also need a return ticket?

Steve_

Not if they have an immigrant visa, or something similar to justify it being one-way. And it's subjective anyway, CBP like you to have a return ticket, but it's not a legal requirement.

GC44

We were toying with the idea of having a return from UK to US but only a single from US to Winnipeg. Anyone envisage any problems with this?

Steve_

It's entirely up to the inspectors at the POE and how good your explanation is. I have done that myself in the past though. Are you visiting Canada or are you moving here?

GC44

Fingerscrossed, moving there.

Steve_

Well if you have a work permit application or an immigrant visa it doesn't really matter, just show it to CBP when you enter the US. Clearly you are not intending on remaining in the US and that is their primary concern.