Could it be because of Russian influence in the referendum?
Yes definitely..Here is response from Canada's president.
"In response to Russia’s unacceptable behaviour, we’re expelling several Russian diplomats from our country. Canada will always stand in solidarity with the UK - and we’re committed to working with our allies to protect and uphold the safety & security of all our citizens."
You can read between lines, he,s really saying May is a bitch and we are kicking diplomats out because they caused Brexit.
Trump has closed Embassy in Seattle..( The Russian one)He,s expelled around 100 diplomats/ staff..
Its largest action of its type in history..all because of Brexit. ( or actually to pretend they think Russians are guilty, in private they are saying different...??? )
Not that Putin will be worried but don't think he expected such a unified response...does make our position a little more secure. Better than us acting in isolation.