The first thing to determine is your tax residency. If you are deemed to be non-UK resident for tax purposes then you may well be able to claim back all of the UK tax and just pay taxes in Canada. You may also not be liable for UK National Insurance Contributions.
Residency can be a complicated area but is primarily concerned with where you live the majority of the time, where you work, for whom you work (and where they are based) and for how long in respect of the aforementioned.