I work remotely for a company in another province — which PNP do I apply to?

This is genuinely case-specific. Some streams count your work experience wherever the employer is, while streams built around an in-province job offer usually require the employer — not just you — to be located in the nominating province. Provinces generally expect you to live, and intend to settle, in the province you apply to, so applying where you physically live is the usual starting point. Check how your target stream defines "work in the province" before applying, because remote arrangements are treated differently across programs.