There is no definition in the Lobbying Transparency and Ethics Act. The Quebec act defines a lobbying activity as a communication by an individual on behalf of their enterprise, their organization, or a client, with the intention of influencing a decision by a public office holder.
Definitions may vary from case to case and law to law. They may talk about contracts or about influencing legislation, regulations, permits or grants. As I said initially, lobbying schemes that I would characterize as "modern" also provide rules of ethics and conduct that mean that lobbyists—the people who perform lobbying activities—must adhere to certain fundamental ethical principles.
I don't know whether you have looked at Quebec's Code of Conduct for Lobbyists, but some of the rules in that code are very similar to the rules in the federal Lobbyists' Code of Conduct. It talks about generally applicable rules of ethics, such as the prohibition against giving false or fraudulent information, the obligation to say who their real client is, or the fact that they must not try to unduly influence a public office holder.
In the case of Quebec, the most important rule in respect of ethics and integrity is not to try to persuade a public office holder to violate the rules of conduct applicable to that person themself.