I haven't seen that poll. Did you say it's an Angus Reid poll?
When you say that they've lost faith in the immigration system.... I would not be surprised by a big jump in trust in the system. That's the kind of thing where a single perceived failure can shift attitudes fairly widely, but on broader measures, such as whether we should bring in more immigrants, how many and so on, that's where I think you see more stability.
To maintain that trust in the system, if that's what you want to focus on, I think the main thing to do is to avoid perceived failures and perceived inefficiencies. That means avoiding real failures and inefficiencies, but it also means presenting the system in the best possible light.