Can I use my provincial nomination letter to extend my work permit?

In many cases, yes. A provincial nomination can support an LMIA-exempt, employer-specific work permit, meaning your employer does not need a Labour Market Impact Assessment. Most provinces issue a work permit support letter on request — you include it with your work permit application to IRCC. The permit is usually tied to the employer and province named in your nomination. Apply before your current permit expires so you benefit from maintained status while waiting.