I'm sure you can mention this in your cover letter if you really wanted, but more likely is that they will need teachers and will ask you in your interview if they're really concerned - the truth is that people switch jobs all the time, some schools are awful and other people have reasons they want to leave.

You will be fine.

There seems to be many, I'd like to increase my chances of getting into a good school with a friendly atmosphere.

I think Americans/Canadians tend to be more relaxed than Brits, so I'd like to jump ship as I only have UK qualifications with leadership qualifications for UK schools. I've never had luck with them, having only ever received interest in A Level and IGCSE schools.

Any suggestions?