You can work full time remotely if your employer is not based in canada. It does not have anything to do with customers being in Canada or anywhere else.
You should just not be competing with Canada's labour market is what they mean.
Having said that, it should not affect your studies because that might affect your study permit conditions.
Source: IRCC
https://www.canada.ca/en/immigration-refugees-citizenship/corporate/publications-manuals/operational-bulletins-manuals/temporary-residents/foreign-workers/what-is-work.html
“Work” is defined in the Regulations as an activity for which wages are paid or commission is earned, or that competes directly with activities of Canadian citizens or permanent residents in the Canadian labour market.
An activity which does not really 'take away' from opportunities for Canadians or permanent residents to gain employment or experience in the workplace is not “work” for the purposes of the definition.
Examples of activities for which a person would not normally be remunerated or which would not compete directly with Canadian citizens or permanent residents in the Canadian labour market and which would normally be part-time or incidental to the reason that the person is in Canada include, but are not limited to:
long distance (by telephone or Internet) work done by a temporary resident whose employer is outside Canada and who is remunerated from outside Canada;
Side note: This is info based on IRCC's website but you should do your own research to come to a conclusion.
Bonus source:
Refer to the 2 replies on this tweet by IRCC. They're not relevant to the original question but might help you make decision!
