I live in Oakville, Ontario.
I'm new to growing spinach, beets and carrots.
Is it too early to plant spinach, beet and carrot seeds now?
Go ahead and plant!
Your seed packet should tell you when and how to plant these veggies.
The most important thing about vegetables is what kind of soil you are putting them into.
all 3 are cool weather plants & can be planted as soon as soil is workable. If it has been dry in your area, soak the beet seeds before planting. You can stagger-plant carrots every few weeks until August or earlier if it remains hot weather.
hope this helps.
Here is a link that might be useful: gardenweb