TLDR: Polls aren't always accurate, especially so far in advance.

Like I said, the polls measure popular opinion. Polls across large geographic areas often don't correlate with riding results - which is what matters in Canadian elections. You would need riding polls to get better predictions. But even then, the results may not be very good predictions of a general election.

Even the best polls will have errors. Voter polls will often have a margin of error between 3-5%. That could already eat the 4% difference between the Conservatives and Liberals. There are plenty of other problems that a 4% difference might not mean much:

• Not all poll respondents actually vote. Looking at US data, it appears that conservative voters are less likely to skip an election than progressives. The most common explanation I've heard for this is that conservative voters will often vote cuz something upsets them while progressives will vote for what they want to see. There's a human nature element to this.
• The "left" is still split in Canada, as mentioned. This is an enormous advantage for the Conservatives. Unless the Liberals and NDP decide to strategically avoid fielding candidates in certain ridings, they will have a very hard time unseating the Conservatives. I've read that this has been discussed, for some time now, but has not gone anywhere.
• The election is still a long ways off. A 4-or-more point swing (in any direction) would not be a big shock.
• Lots of people screen phone calls. Entire demographics can be missed by these polls.
• Poll respondents can answer more progressively when it's just a poll. When push comes to shove, ie they cast their ballot, such respondents can get more conservative. My understanding is that voting more conservatively than a poll response is much more common than the opposite.
• The Conservatives still have plenty of time to curry favour with the electorate with per-election goodies.
• Attack ads can be effective. The Conservatives have shown that they are not afraid to use them. If the polls are too close, it could get nasty.