Welcome to the Forum. I assume you mean July of 2020.
AFAIK, the "Preparation of Marriage" visa is only if you're going to get married here in Switzerland.
If you're getting married in Canada but you want to move here earlier, the only options at the moment are 1) to apply for a concubine permit, if the canton where she lives even offers it. She signs to be responsible for you for 5 years, even if the relationship later falls apart. You won't be allowed to work or 2) get a job on your own merits where the employer sponsors your permit.
Otherwise, you keep visiting under the 90 days in/90 days out rule.