It costs about CAD 100$ to apply and he'd need his mother's original Canadian birth certificate... if he sends his documents directly to Canada House, for a fee they'll make copies of it to send in and return the originals to him - this saves the hassle of his having to get it all notarised. Once everything is in order, it goes to Ottawa for processing and, upon successful application, a letter and a certificate are sent back to him. He'll need the certificate when he applies for his passport (which can also be done from Canada House)... one word of caution, OP... the cost of a 10 year passport is an eye watering CAD 260$/GBP £150 and once you've received your certificate of citizenship, you'll have to enter Canada on a Canadian passport, each and every time you enter Canada (yes, it's a money grab).
When I registered my daughter back in '16, I sent in her paperwork in late August and received her certificate just after new year in January '17... the paperwork had arrived in London just before Christmas, but because of the holidays, it was January before she received it.
Please do not send me PMs asking for immigration advice on posts that are on the open forum. If I haven't responded there, it is because I do not have the answer. I am a moderator, not a legal professional, and as such I can only offer an opinion and not advice.
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