Upvote:1
As per the answer to Do I need a US visa to transit (or layover) through an American airport? you will require an ESTA (similar to a visa, but obtained electronically) before travelling the US, even though you are only transiting through the US. ESTAs are relatively easy to obtain (presuming you do not have a criminal record/etc), and cost only $14 per person.
UK citizens do NOT require a Visa or anything similar to transit Canada.