The Queen of Canada must provide royal assent for legislation to pass.
The Governor General of Canada is her appointed representative who acts on her behalf.
The Queen of Canada also happens to be the Queen of the United Kingdom.
Canada could, if they wanted to, pass a new Succession to the Throne Act which could change who inherits the crown.
If Canadian laws surrounding the order of succession were different to the UK, the monarchs of the two countries could diverge. Canada's Canada Act 1982 prevents the UK parliament legislating for Canada, which since then means if the UK changes succession to the throne laws, Canada has to mirror it in their legislation, or they will potentially have different monarch. Canada had to do this a couple of years back when the UK changed the how the crown was inherited (made the oldest child of the monarch inherit it, regardless of sex ... I think)
