How do I claim tax reimbursement for purchases in another country?

Hi Reddit, I've been visiting Europe (UK and Belgium) for the past week, going home to Canada shortly. Given the season, I've spent quite a bit on Christmas gifts and the like, and its come to my attention that I can get reimbursed for the sales tax I've spent. As rates are particularly high (20% versus 13% back home) I would like to file the appropriate claim. However, I have no idea where to begin with either of the Canadian, British, or Belgian governments. Reddit, how do I go about getting reimbursed?