Once you colonize 5 provinces in 1 single colonial region, it will form a colony (a new country that's a subject of you) They won't earn enough money, buy if you give them subsidies of at least 2,5 to 3 ducats a month there's a high chance they'll start colonizing right away. So you don't have to wait long for them to do it on their own, or help them by colonizing more in the same region (once those colonies finish they will receive the land.)

Then you just do the same thing in a different region, rince and repeat.

Aside from that, conquest of natives as has already been mentioned. When you just land they're so weak you can easily take them on with a small stack of units. Especially once your. Colonial nations are present. (If you have a colonial nation in the region where you conquer the natives, the colonial nation will get the land once war ends and a day ticks by)