Is he remaining a resident of BC? Or will he change everything over to Alberta (health care card, drivers license, etc).
If he changes his official residence to Alberta, on return, he will pay no tax under the New West Partnership Trade Agreement .
See page 8: exemptions.
https://www2.gov.bc.ca/assets/gov/ta...8-vehicles.pdf
and
https://www2.gov.bc.ca/assets/gov/ta...-residents.pdf
and if he plans on maintaining his residence as a BC resident I believe it is 10% he would pay.