The client landed in Dec 2019 with family for two weeks and went back home with the intent to come back in Mar 2020. Covid situation disturbed their plan and husband landed in July 2020 followed by family in Jan 2021
The obvious resident ties established in this case are in July 2020 but can the client file for 2019 as well since they intended to make Canada a new home and CoVID upset the plans? they applied SIN, driving license etc when they arrive first in 2019
In your files you have a copy of his foreign tax return that he filed (and that his spouse filed), and had assessed, certifying and notifying that country of his tax emigration exact date for that country, yes?
So look in your files for that date, and then also examine the tax treaty for that country.
Alternatively, refer the client to a colleague who deals with dual taxation in both of those countries.
Caution: if the taxpayer is trying to get (2019) tax credits that it turns out he knew he is not entitled to, S238/239 provides for severe penalties, including jail time.