1) My brother is a Canadian citizen who was admitted to a PH.D program
in the US and will begin school in September. As a Canadian citizen, I
believe he would not need an F-1 visa as there is a visa waiver
program in place, but would like confirmation of this particularly
because I keep reading personal stories about Canadian students with
F-1 visas.  If a Canadian student does not need an F-1, but simply
needs a SEVIS form: how is this obtained?

2) The complicating factor is that he wants to marry his fiancee (a US
citizen) in August of this year. Will he need a K-1 visa since he has
an alternate legitimate reason for coming to the United States to
study? If not, how does he adjust status after he marries since he
should be coming in on a visa waiver?

Dear mtvlagunacar-ga -

Thanks for using Google Answers.

Many Canadian citizens can travel to the US without a visa.  However,
if your brother is a fiance of an American citizen, he would be
required to obtain a non-immigrant visa.

This is what the US consulate says:

"Canadian citizens do not require visas to enter the U.S., except when
coming as immigrants (permanent residents), or in the following
non-immigrant categories: Diplomatic,... Treaty Trader/ Treaty
Investor,... Fiancé(e) of U.S. citizens ("K1/K2" visas), or spouse of
a U.S. citizen (K3/K4 visas)."

http://quebec.usconsulate.gov/content/textonly.asp?section=visas&document=canadian#WHTI


To make an appointment for obtaining a visa,  your brother can
telephone the numbers on the following web page:

http://canada.usembassy.gov/content/textonly.asp?section=travel&subsection1=usconsulates&document=montreal

Canadians are permitted to study in the US (without a visa) but must
have a valid form I-20 (Certificate of Eligibility):

http://www.voyage.gc.ca/main/pubs/PDF/usa_bound-en.pdf    (scroll
midway down  page to "Studying in the United States")

As you can see, entering the US for the purpose of study implies that
a student has no intention of immigrating and every intention of
returning to Canada.

An example of the I-20 process can be found at:

https://www.hvcc.edu/international/obtaini20.pdf

I am neither an attorney nor an immigration expert.  An immigration
attorney may be able to find loopholes or advise you differently, but
my reading of the information cited above is that your brother would
probably be safer with an immigration (K-1) visa if has the intention
to stay in the US.

All the best,

Alanna-ga

Google Search

https://services3.cic.gc.ca/ols/ols.do 
http://www.cic.gc.ca/english/index.html
http://www.cic.gc.ca/english/contacts/index.html
These are the Immigration websites for the Gvernment of Canada.
If you can't find the answer on the first two pages the third gives
you cntavt information.