Democrat-leaning Public Policy Polling finds the Minnesota marriage amendment leading in the polls (PDF results here):

Should the Minnesota Constitution be amended to provide that only a union of one man and one woman shall be valid or recognized as a marriage in Minnesota?
Yes - 48%
No - 44%
Not sure - 8%

We've found that those who answer "Not Sure" tend to vote to protect marriage when given the privacy of a voting booth.

On the leading question "Do you think same-sex marriage should be legal or illegal?" Minnesotans respond:

Illegal - 47%
Legal - 43%
Not sure - 10%

Another interesting factoid: 34% of self-identified Democrats in Minnesota don't believe gay couples should be allowed to wed.