My experience is that you will not be able to choose the 32-bit version at installation (it tells you that you must use the 64-bit version instead). The 64-bit installer will then install both the 32-bit and 64-bit version and will then set the 32-bit version as the default.
However, note the issue/bug I'm running into where it then afterwards wants to change the default to the 64-bit version. I can't believe I'm the only one running into this issue. My system is pretty typical, and I have not made any weird tweaks. I also don't even have any other browser installed.