Royalex canoes are much “floppier” than composite boats so some visible flex of the hull bottom is not necessarily an indication of a problem. This will vary with the length of the boat, the contour of the hull bottom, and the thickness of the Royalex sheet that the maker speced for the hull. A hull with a more rounded bottom will have more inherent rigidity, like a cylinder has. A hull with a flatter bottom will tend to flex more.
The specs that I found for that model list a weight of 72 lbs. That would be a fair bit for a composite boat, but for a 17’ Royalex canoe with a center depth of 14.5", 70 lbs is really not all that much.
As for racing tips, any racer will tell you that the key is paddle cadence. In other words, keep your strokes short and do more of them. The shorter your paddle stroke, the more you will be able to keep the paddle face perpendicular to the surface of the water for maximum efficiency. The farther back you carry your stroke, the more energy will be wasted by trying to lift water with the paddle, and the more yaw your stroke will tend to introduce. For most paddlers, this means taking the paddle out of the water considerably sooner than you might do naturally.
You and your tandem partner might want to try the so-called Minnesota switch or “sit and switch” technique. This is the most efficient way to propel a tandem canoe. The canoe is steered basically by both partners switching paddling sides simultaneously before the canoe has yawed significantly to the on-side. In tandem paddling, the on-side and off-side are defined from the perspective of the bow paddler, so if that person is paddling on the left side of the boat, the port side is the on-side and the starboard the off-side. The boat will ordinarily want to steer toward the on-side for reasons that have already been mentioned.
Any corrective strokes used to steer the boat will detract from maximum efficiency whether that be a J-stroke, Canadian stroke, pitch stroke, or whatever because anytime you are applying the correction, you are not providing maximal power for forward propulsion. So with the sit and switch technique, both paddlers do nothing but forward power strokes, unless some sudden unanticipated maneuver must be undertaken to avoid hitting something, or to make a tight turn. The stern paddler is far and away in the best position to judge the heading of the boat, looking down its entire length, so the stern paddler generally calls the switches and each paddler might do something like 5-10 strokes on each side (and you don’t necessarily do the same number on each side) before switching, depending on boat design, wind conditions, etc.
Traditionally, the stern paddler calls “hut” to indicate a switch and both paddlers switch sides simultaneously upon the recovery phase before the next full stroke. And yes, bent shaft paddles will be more efficient, especially for seated paddlers.