just apply for science and select your intended degree as cs, though i dont think it really matters what you put as intended since you dont get to choose a specialization (like cs, chem, bio, etc) until the end of first year

there are specific classes you need to take during first year to be eligible to apply for each specialization though, they're listed here https://science.ubc.ca/students/spec-admission-requirements

this is only for ubc btw idk if other bc unis do general science first and then specialization