Transport Canada classifies swim boards as human-powered vessels if you are using them to take a trip or do a circuit such as a group crossing. Therefore, you must have a Canadian-approved lifejacket or PFD on board which is available for immediate use.
Many PFDs such as low-profile vests and waist-pack inflatables are easy to use for swim boarders.
Note: The Substitute Safety Equipment provisions in section 4 of the Small Vessel Regulations do not allow leashes in place of lifejackets and PFDs. They only allow like-to-like exemptions, such as high-buoyancy PFDs instead of small vessel lifejackets on certain types of vessels.
Transport Canada supports leash use, but not as a replacement for lifejackets and PFDs.