It might depend on the year. Some years ago when there was a foot-and-mouth pandemic in the UK, they were stricter on entering Canada than they are usually (including a mat for everyone to walk on).
Once (maybe a different year) I entered with muddy hiking boots. They immersed the boots in something for me (formaldehyde perhaps) and gave them back to me in a sealed plastic bag … I expect they would have been within their rights to confiscate and destroy them, though. Since then, obviously, I scrape and rinse any mud off them before flying.
According to the Canada Border Services Agency:
Many different kinds of items can introduce foreign threats into
Canada. These include things as diverse as:
- Food, such as raw or cooked meats, fruit/vegetables, milk;
- Homemade articles, such as items made from plants or wood;
- Houseplants;
- Live animals, including pets;
- Firewood;
- Plant cuttings, seeds; and
- Muddy hiking boots.
…
Be sure to clean all soil and organic debris off of any items
including hiking boots, vehicles, boats and gardening and construction
tools/equipment.
They might throw them away if there is enough mud on them to cause the agent to be concerned. To be safe, just wash your shoes before you pack them.
Credit:stackoverflow.com‘