Should I cancel this card?

Zola.

I have a basic Santander credit card that I have used maybe twice to book flights with in the past 3 years.

I have a Santander 123 credit card that I buy fuel and shopping with for the cashback incenctives and pay it all off 100% every bill date.

I am going to a mortgage broker next week for an initial meeting as a first timer, and I was wondering if I should cancel this unused card in advance of any credit checks etc ?

grumbler

This depends on the credit limit. If it's big, then it's worth closing the account. However, this will have effect only after the CC company reports it to the CRA(s).