Other than being a bit heavier than normal, I don't think an oak mast would give you any problems and it's probably short enough that the increase in weight aloft wouldn't be much. As for the yard and boom, oak and ash can be used in a pinch, but they may be surprisingly whippy as well as a bit on the heavy side. If I could find a couple hunks of spruce or fir (maybe even closet pole, if I could find a couple good ones) I'd be inclined to try it first. It's usually a bit stiffer and lighter. Excessive spar bend is always one of the biggest problems to try to get some control over with long-sparred canoe sails. It makes it difficult to cut a sail that works reasonably well in a variety of conditions, so the stiffer, the better.
On a sail of that type and size, I don't think you really gain much by going hollow on the spars - at least not enough to justify a lot of extra work, so I'd probably build them solid. If you do want to experiment with hollow construction, I'd use a different method. Shortly after "Canoe Rig" came out, a new method of hollow spar building began to show up. It's called "Bird's Mouth" construction and it's pure genius. If you'll do a search on the WoodenBoat Forum you should find some threads on it with photographs of the process. I've had several customers build tapered hollow spars with it and they came out great. None of these people had any previous spar-making experience and I think they even had fun doing it.
Essentially, you glue-up the mast from strips of wood (eight of them, I believe - usually cut from a couple of carefully selected 2x4's, fresh from the Home Depot). They're not too different from canoe-building strips. Then you cut a V-shaped notch along one edge of each strip. The opposite edge is left square. Tapers are made by trimmimg the squared side, Then you grab a bunch of rubber bands and glue the square edges into the V-notches of the next strip over. This probably sounds crazy, but when you see the photos it will quickly make sense. When the glue dries, you have a nice, tapered, 8-sided spar. You can then round it out where desired and plug the ends. There is no hunting for perfect wood and most of the shaping is done by the process. I have no clue who developed the technique, but it's a tremendous contribution to small boat building. Whether you decide to go hollow or not, hunt up a good photo spread on this method. Sooner or later, you'll likely want to try it for fun if nothing else.
