The folks at SUSA asked about one constitutional amendment that's already on the ballot and two that seem like they're destined for that same fate.
SurveyUSA (2/3, 11/8 in parenthesis, 5/25 in brackets):
"An amendment to the Minnesota Constitution on the ballot defines marriage as between one man and one woman, will you vote..."
(MoE: ±4.3%)
For 47 (46) [51] Against 39 (40) [40] Not vote 10 (10) [8] Not sure 4 (4) [2]
This issue has essentially stabilized over the last six months, with amendment supporters holding a small but consistent ~4 point advantage in the average of polls. SurveyUSA though is the only pollster who has given respondants the option of not voting for the amendment and they find 10% who utilize this option.
Those not votes, by people who cast a ballot, will count the same as no votes so it's tempting to simply lump them together and say that the amendment is actually losing slightly 49-47.