Tomb Raider: Definitive Edition is currently $10.49 at PSN Canada. Adopting PCGameSupply's exchange rate of $20 for £11.99, that's £6.29.
Better still, using the PS+ trick, you can save a further 10% off the headline price of $34.99 i.e. $3.49. Take that from your $10.49 and that leaves $7, or £4.20. Lovely.
To get a free 2-day trial of PS+ (once per account), simply sign into your Canadian account and try to upload a save file from the Settings menu. You'll see a message saying that this is a feature of PS+; here's two days free!