Hi, I’m Brazilian and I am traveling to Vietnam from Cambodia via land border crossing. Can I get Visa on arrival?

No, Please be kindly informed that visa on arrival is for those traveling to Vietnam by air only, so you cannot apply for this kind of visa.
In this case, we suggest you to visit the Vietnamese Embassy in Canada to apply for the visa.
Hopefully this information is clear to you. Should you need any further information, please feel free to let us know.