Sorry, I’m not sure how it works in Canada, but I’ll describe how it works in the USA (just in case it gives you some ideas). Feel free to ignore this post if you’re looking for specific websites as opposed to an overview of the process.
Short answer: Various government bodies, non-profits, industry groups, trade journals, and local papers will tell you about things that are happening. None of them will really care about your opinion unless you’re rich and powerful.
We have a tiered system here. Congresspeople make federal law that supersedes everything. States have their own legislatures that make their own laws. They delegate some of their authority to counties (blobs of land smaller than a state), which then further delegate some of the details to cities (smaller blobs of inhabited land). At each step of the way, there is usually a website detailing the latest discussions and a list of new ordinances. In the USA, most government meetings are required to be open to the public. Anyone can go and listen and provide feedback and then be ignored.
The hard part is hearing about new things to begin with. Area newspapers are usually the best source for that, because there is no overarching system to inform citizens of all new and changed ordinances at every level – we’d all become full-time lawyers if that were the case. However, there are a lot of websites, both from the government itself and outside parties (biased or otherwise) who track the passages of various proposed laws from inception to enactment. You can see a proposed law’s status pretty much every step of the way.
To use your examples: For local bike laws, I am a part of the local bicycle commuters’ association, whose monthly newsletter tells me about pertinent changes (if I cared to read it). Occasionally the topic comes up for discussion by my City, and I can go to their council meetings and tell them I want more bike trails. They’ll listen and give various reasons about why it’s not so easy. Then I can take my same concern to the County meeting and tell the supervisors there the same thing, and they will mention things like rights-of-ways bought by the railroad industry and the budget cuts and basically tell you to shut up and suck it up. Occasionally, over the course of a decade or more, really concerned citizen groups can raise enough money to seriously pitch a project to these bureaucracies and pressure them to do something more. Generally, though, citizen concerns don’t really matter unless you’re rich or locally powerful.
For things like digital rights, in the USA that is bizarrely governed by an ancient part of our constitution that gives the federal government rights to regulate interstate commerce. They do a mediocre job of it, with agencies like the FCC basically maintaining the physical spectrum for maximum profit and not maximum citizen value. Edit: First Congress will pass various laws written for the benefit of the telecom industry. Then the Supreme Court will, upon suit, examine them for free speech and copyright issues, which is what most digital rights come down to. Citizen input to these entities are usually ignored. There are outside groups like the Electronic Frontier Foundation and the American Civil Liberties Union that will instead fight for citizen rights on your behalf, to mixed effectiveness. Finding out about new changes in the digital realm is easy – just subscribe to various tech blogs like Slashdot or Reddit. To be able to affect policy, though, you’ll have to be at least a multimillionaire (or apparently a cyber-spy).
For things like chicken health, various non-governmental groups will usually be very interested: the local equivalent of PETA, the poultry processors, the ag department of your state/county, your local agricultural extension (farmer support organizations set up by universities and the like), industry journals, etc. You can seek out membership in any of those organizations to be kept abreast of changes. For the antibiotics thing, it seemed like they preempted governmental action by doing it voluntarily first. There was probably discussion in the industry that happened before then, and you can look for trade journals or online forums frequented by people in that industry.