Talking about statistical theory and polling strategy effectiveness is all fine, but here's some real-world results:
Last federal election, the
results for the 3 major parties by % were:
CON - 39.6%
NDP - 30.6%
LIB - 18.9%
Now, here's a summary of
polling around the 2011 election. In the immediately preceding days, the polls were a couple points off, but close. You can decide for yourself whether that is close enough to consider modern polling, even with its inherent biases, accurate.
However, you can also see a long term polling summary from 2008 to 2011
here that shows the inherent danger of reading anything into polls this for from ballot day.