You would need to bring a claim against your aunt for conversion and breach of contract. If the amount in question is less than $25,000, you would want to bring the claim in small claims court. You would explain to the court that you lent the money (it was not a gift) to your aunt, and that you expect to get it paid back. You can also ask for interest (though a judge will want to know if this was agreed on beforehand). From the date of judgement, you can ask for interest to accrue from that date.
In terms of how to file a claim in small claims, here is a site that walks you through it.
While the rules may be slightly different depending on which part of Canada you are in, this will give you the information on how to proceed. Of course, if you feel more comfortable hiring an attorney to help you, that is entirely up to you, however, you should know that this is only really worth it if the amount in question exceeds $5,000.
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