I was going over UBC’s requirements for admission to Faculty of Science programs and found out they require maths in the XII Standard as prerequisite. However I chose biology over maths in my XII Standard(You get an option between the two). Do all colleges(Both USA and Canada) require me to have maths as a subject in my XII standard for admission to any science courses? If so, is it possible to take admission in an arts program and then transfer to any Science course? I plan to apply to med schools. So I need those science credits.
Each university sets its own admission criteria. There’s no country-wide minimum math requirement to gain admission to a science major.
The procedure to change majors after you are enrolled depend on the university as well. In the US it is often easy to switch majors within the same organizational unit of the university (e.g. within the School of Arts and Sciences or within the School of Engineering) but that may not be true for any particular university or major, so do your research.
As an international candidate, your options will be extremely limited for med school if you plan on applying to US or Canadian med schools.