Your tax residency status is based on the criteria set out in the residency rules here:
RDR3 Statutory Residence Test
If you are classed as both UK resident and Canadian resident then you will need to look at this guidance to see which country takes precedence:
Dual residency (Self Assessment helpsheet HS302)
You would only be required to complete a UK Self Assessment tax return if you are classed as UK tax resident and you have income from abroad i.e Canada.
Please see guidance here on self assessment criteria:
Who must send a tax return
If you were UK resident with no foreign income, then there will be no requirement for a tax return.