All other things being equal .. cash is less cost for your parents.
A cheque, even a draft, drawn on a Canadian bank would have to be remitted back to Canada for value. This means, for you/them, cost. Cash, on the other hand, will get the Bank's buy rate on the day, which would include the Bank's margin.
The drawback with cash is the security involved in getting it to Ireland safely.
There are other methods for transferring funds, e.g. Western Union. In other words, your options aren't limited to banks.