There have been many scams involving Canada Revenue Agency (CRA).
Scammers may call you and tell you they are with CRA. They will say you owe taxes and may even threaten to send the police. They try to get you to send them money. They will ask you to send them gift certificates. This is a scam CRA will not act like this. CRA will send you a letter before any collections actions are taken. If collections action is taken they may seize your bank account but will not threaten to send police.
You can make payments to CRA through your bank. Many banks allow you to make payments to CRA online. For more information on making payments to CRA see their website: http://www.cra-arc.gc.ca/mkpymnt-eng.html. Gift cards is not on the list.
If this still of a concern you can call CRA and ask if you owe any money. CRA can be reached at 1-800-959-8281 for individual inquiries and 1-800-959-5525 for business inquiries. They will ask you some questions to make sure of your identity. It may be easier if you have your last notice of assessment in front of you when you call. They will probably ask you the amount on line 150 of your personal tax return for example.