Unfortunately unlike the USA where all aircraft liens have to be registered with the FAA Canada does not do this . To be totally 100% sure there are no liens on a Canadian aircraft you must do a search with every province the aircraft has ever been registered in. This can be done with "Ministry of Consumer and Commercial Relations Personal Property Security Registration Branch (PPSR)" for about $20Cdn over the phone. For Ontario the phone number is 1-800-267-8847 (416-325-8847). You must have the owners first and last name, serial number and any other information like address and a SIN # makes it even easier. They will tell you about the couch they haven't paid Leons for, the '95 GMC truck, etc etc. If you want a printed copy sent to you of the lien search it will cost you a little more and they take credit cards over the phone.
The more reassuring side of things is that is is VERY hard to get a bank to lend you money to buy an airplane in Canada... so very rarely is there a financial lien against one and in the case of the guy borrowed money from his brother-in-law etc these types of loans are rarely registered. If not registered there's not much to worry about. 10 years of buying and selling aircraft from all walks of life I have only had one that I had to have a bank "release all interest in" and this was a purchase from a flying school that was in hock!