There is a cabinet directive for departments to perform strategic environmental assessments, so whenever there is a proposal they have to do an environmental assessment. This is done through a cabinet directive. This is one avenue that could be taken to force GBA to be performed, through a cabinet directive.
There are many means by which you could do that. It seems to work for the environmental assessment. It might work for gender-based analysis, but it's up to the government to decide how they would approach this: through a cabinet directive, a formal policy, or individual departments selecting their own means to perform GBA.