With a Canadian husband, your wife has little chance of being approved for a TRV. It's possible if she can show VERY strong ties to her country but the majority in this situation are refused.
If she gets a TRV and comes to Canada, you can file an inland sponsorship app along with an Open Work Permit app. Including the OWP app will allow her to remain in Canada throughout the process; it takes about 4 months to get the OWP.
However, if the TRV is refused, you will need to file an outland app.
Visa validity has nothing to do with length of stay. Visitor status is granted at the border by CBSA, who decides how long the person may stay.
Those who include an OWP app with their inland app do not need to apply for any other extension. The OWP is granted after about 4 months.