Unless you have some grown children or grandchildren willing to sponsor you for supervisa, you should forget about it because supervisa is really only for parents and grandparents.
That leaves you applying for a TRV (visit visa) which is in a couple of ways different from a supervisa. For one, you don't need to be sponsored for it and for another, it allows you to stay only for 6 months at a time although you can apply to extend that period once you are in Canada.
You can apply for jobs and do interviews while in Canada on a TRV. You should however probably not mention that when you enter or they may think you plan to work illegally and refuse to let you enter.
Any type of trial employment would be illegal. If paid, it would be a breach of your TRV which is a visit visa and does not allow you to work. If unpaid, it would be a breach of labour laws that stipulate that any worker should get paid minimum wage.
If you do manage to find an employer who is interested in hiring you, you would have to leave Canada in order to get the work permit. The employer first needs to apply for the LMIA and unless you are visa exempt to Canada which you probably aren't if you are asking about a supervisa, you would have to apply for a work permit in the Canadian embassy in your home country, proving to them that you only intend to go to Canada to work temporarily and will not overstay your visa. If you are visa exempt, you could apply for the work permit on entry so you could leave and come right back. You are however not allowed to apply for a work permit from within Canada except under special circumstances like for example if your spouse is a student in Canada or you are extending an existing work permit.