I just bought a 1.5m kayak that I'm going to use this summer. I'm planning to load it on my Sierra but not sure if I should install a headache rack to safely secure the kayak or extend my truck bed. Any advice?
1.5M = ~ 5' That should fit in the bed. If you have a 4 door with a short bed might look at a bed or tailgate extender. Or prop it up on the tailgate. Will it fit diagonally? If you go with a headache rack it is not long enough to reach a rear support from the receiver hitch and not really long enough to reach a rear mounted ladder rack if its a 6' bed. If you are by yourself it will be easier to put in bed I think.
If you have a 6' bed a track rack type rack that can mount anywhere along the bed rails would be good. Or any universal type rack and use several C-clamps to attach to the bed rails (then use rope or straps to secure forward and backward and brace it).
You shouldn't have to worry about this but one thing to watch out for in general carrying canoe's is any curve to the bow or stern lines needs to clear the roof of the truck when on a ladder rack type carrier. I built a wooden ladder rack that was a little higher than most for a canoe with a lot of curvature (think its an older ole towne Guide canoe).
If you are going to carry a bunch of camping gear or other stuff you might need a rack otherwise you could just tote it in the bed.
I have carried a 17' canoe on a Mitsubishi regular cab with just foam blocks on the roof and a bunch of rope tieing it down. Looked funny like a giant long hat (longer than the pickup truck) and caught wind passing big trucks but I drove on interstate w/o a problem. The foam blocks had to be near the front and rear of roof. They would cave in the thin sheet metal a little.
Took me a while to find this picture. I made this rack for a weekend camping trip a few years ago. I wish I would have made it out of steel. Even tieing canoe to the truck bed with lots of rope and ratchet straps I still don't like trusting a wood rack but I was in a rush and this was my easiest option at the time. A plain headache rack would not allow it to clear the roof while upside down and that is how I like to carry them. You'll want enough clearance so when you pick up the rear end it doesn't see-saw pivot and scratch the roof of truck.
It is an older Old Town Camper canoe ~17 ft and the ends curl up a good bit.