yes you can. Actually in years before electricity and central heating, gardeners and farmers would often start sowing their vegetable seeds under a cold frame just about now - especially in your zone which is 3.

So what do you wish to plant? annuals, perennials, vegetables?

I like to throw breadseed poppy, flax, black eyed suzan and other hardy flower seeds. The poppies I discovered quite accidentally when the seeds from pods threw out in the fall grew and bloomed in June, while the seeds planted in the spring bloomed in July. I now sow them early and get a wave of red all summer long.

Perennials that don't need a cold treatment and or hardy annuals.