I work in the lumber industry but I am in no way an expert on this. Often times loggers would engage in "log driving" which means they'd tie a bunch of recently cut trees together and guide them downriver to a mill or port. I think it would be more practical to ship them overseas as logs instead of cut in any way because the way a log is sawed dictates much of the use. So, say a French Canadian outfit wants to ship lumber to Paris. They wouldn't cut it in to 2x4s in Canada because what if the customer wants a 2x6? Or wants to use the log for a telephone pole-like post? There would be months of lag time in between when an order came across the ocean to when it arrived at its destination and once wood is cut and sawn into boards, it does not last forever.

A big sailboat needs ballast- something heavy in the bottom of the ship to keep it upright when the wind is blowing. Heavy cargo of many kinds could do that ( barrels of wine, say) but timber needed little protection, compared to barrels of flour, and could go down low. Perhaps someone else knows just how often it was sawed into beams or planks, or simply left as logs. It would be easier to pack a hold tight with planks than with logs, so likely the former. Straight, tall big pines were being marked in New England in the 17th century for special use of the British Navy for masts, and of course when those were transported they were left as peeled logs.