most of the claimed waterproof daypacks are of the vynil roll down top variety - I have one (cheap) I bought from Sierra Trading Post - bought it thinking I'd be using it on local day trips and overnighters, but I haven't really used it.
One issue wtih that type is typically no hipbelt, so not the most comfortable carry if heavily packed.

hate to give up the utilty of the "bookbag" with multiple pockets - so I just stick with the one I have and use a trash bag liner - nothing in there that water would really hurt anyways.

to me, for Quetico trips, a "daypack" is too small - I prefer the smaller back pack style (ultralight day and a half type)which has a comfortable hipbelt, a top flap pocket for stuff I want handy, and outside mesh pocket where I can restuff the raincoat if it stops raining - features not to be found in the typical waterproof daypack.  for solo trips, it is my food pack as well.

at 2500 to 3000 cu in size, this isn't just for odds and ends but is one of two main "packs"(the other is a duffle bag) when I solo, or we bring two plus one big pack if my brother comes along.

waterproof - not,  so I just use trash bag liners or waterproof pack liners (the pack and liner weighs less than vynil daypack and holds more) and everything is packed in multiple layers of plastic bags anyways

even with a waterproof roll down top vynil dry bag, I always use at least trash bag liner as a backup in case the pack got holed - and the roll top can/will tend to suck in some water if left sitting in a puddle anyways.  for just rain protection, spraying some waterproofing on the bookbag will work for a while

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somethin like this Hurley pack might fit your needs - at least it has some outside pockets, but I'm not sure of the lifespan of waterproof zippers  pricey at $170 for a daypack

I thought that maybe there would be something good designed for canyoneering, where you often have to swim slot canyons pushing your floating pack ahead of you - but couldn't find anything out of the ordinary - still seem to need the roll down vynil type of pack

Outdoor Research makes some good ones.
SeaLine too.

I have a Granite Gear thwart bag that's waterproof and helps keep things organised and out of the bilge.  Clipped on a shoulder strap and it's my day-bag.

I have one of (You need to Login or Register to view media files and links).  Tackle box, sunscreen, depth finder, towel, etc... all get thrown in after a day of fishing and tucked under the canoe at night.

Hi,

Up in Canada the MEC brand dry bags are good, durable and cheap - I have the 5, 10 and 20 L bags are awesome for day tripping. They are the roll down ones. A clear one enable me to know I have have actually put in the darn bag.  

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My waterproof bag. It has two pillows inside, the front of the pack is clear vinyl so you see the white pillowcases through that.  A ruler is in front for size perspective.  Easy access via a zippered opening, but I do not know how well it would keep out water if the pack was capsized into a lake.  In the rain, it has kept stuff dry.

I bet you could use Azalea's bag as a pfd.  Those look like the same zippers found on a drysuit.

Today my new Gossamer gear Gorilla pack arrived.  It is mostly a one big pocket type of pack.  I plan on using it as a second pack more than a day pack.  For me the one big pocket is not a problem.  You may want separate pockets to keep gear sorted.   It is light and carries a 30+ LB load very well.  I will be able to ware it while carrying the canoe. Check them out (You need to Login or Register to view media files and links)

Sierra Trading Post has a Columbia Dry Bag Backpack (You need to Login or Register to view media files and links)
(You need to Login or Register to view media files and links) $74.95

Was surfing for another tent and came across this water proof bag (You need to Login or Register to view media files and links)  holds 27 liters