The key is to get a visa. Once you have a visa, you can switch jobs easily. The way the Japanese visa system works is that you need a sponsor (your employer) to get a visa, but once you have the visa you can switch employers without a problem. Then when your visa runs out, your employer at the time can sponsor you. Unlike the U.S. (don't know about Canada) where visa holders are beholden to their sponsors and losing the job means losing the visa, Japan allows the visa holder to keep the visa even if he switches jobs.