Yes you can, although they can also purchase it at specialist shops in Canada. My wife's ex-husband's sister's brother-in-law had some at a wedding over there a few years ago, I'm told. When I lived in New Jersey, there were some shops that had Vegemite stocked as well, although at that time, there was no Marmite in the shops. So it is available on the other side of the pond.
If you ship it, make sure you explain exactly what it is however. My ex-father-in-law, brought some Marmite over to me when I was in the states, as my ex and I loved Marmite... While I realise the two are not the same, they have similar consistency. When the customs men in the US opened his bag, they looked at the round bomb like jars, and asked him what it was. He told them it was a food product that was often used in the UK. One custom man opened a jar and took a spoonful for a taste. They kept him under observation for several hours before the British Embassy confirmed that it was really a food stuff.
Then again, when I was in the USAF, a friend of mine had been stationed in Australia for a while, giving support to the F111-D's you had out there. He told me that his first taste of Vegemite ruined all chances of him enjoying Marmite. He asked one morning at breakfast what Vegemite was. He was told that it was like Apple Butter, as it was spread on toast. So he spread the Vegemite on toast, just as he would Apple Butter, thick. It was only after the first bite of course that his colleagues mentioned that it should be spread thin.