Yes, it should be possible. You don't really choose your major until the end of first year (in March sometime). If you can, take the required courses so that you can enter Life Sciences by the time you're in second year.
http://registrar.mcmaster.ca /CALEN...nt/pg1954.html
Click on one of those links you find here to find out the required courses in first year, but also try and keep up with your requirements for the BioTech program.
If you can't switch into Life Sciences by the end of first year, you can still do so the next year.