I am trying to find out whether I have legal recourse to have my
hardwood (tongue-and-groove prefinished) floor repaired or replaced
by the manufacturer, installer, or general contractor.  I live in
Ontario.  I am mostly concerned that the 25-year manufacturer's
warranty specifically declaims damage due to water.
(see the warranty here: http://www.muskokaflooring.com/warranty.htm)

It is my belief that the floor in question was manufactured with a bad
finish.  The floor installer has said previously that he thinks the
finish is fine.  The general contractor, however, has agreed with me
that something seems wrong with the finish, and asked the floor
installer to re-visit and see what can be done.  This will be
happening on Thursday.  If possible, I'd like to learn where I stand
legally before then.  Ideally, I'd like a legal overview with 
URL citations please.

The floor was installed 18 months ago, and has steadily shown to peel
on the edges of boards under what I would consider normal use.

If you need more particulars, I can try to clarify!  Thanks.

Well,

 I do not know if this may help, as
 in my case,some factors were different:

it was not hardwood but a floating floor,
it was not Ontario but California
and it was not a water damage

but problem was similar,
 edges rising up, due to some defect in material.

Lawyer told me I should sue all three

 the manufacturer, installer, and general contractor

(installer was subcontracting)

 Letter to manufacturer, 
 asking foran address where to serve the legal papers 
 plus mentioning legal action to the other two was enough.
 Floor was replaced for no charge.

One important step: After the complaint, manufacturer sends is an
 independent expert to evaluate the claim. That was in our favor,
 but nothing happened until I wrote that letter to manufacturer ..