Because the signs are hand-painted, there's some variation, but generally the Green Party name, and in some cases the logo, are pretty recognizable. So much so that my first thought when I saw one of these signs from a distance was "Why is Akpata trying to pretend he's running for the Greens?" From up close, it's easier to see that these are old Laxton signs from the Green Party of Ontario, not the federal party. So my second thought was that this was quite resourceful, and a good way to re-use the material. But my third thought was to wonder if it was legal.
I don't think it is. The Canada Elections Act requires that election advertising indicate who authorized it, and these signs do not. (The statement of authorization by the Green Party of Ontario is obviously invalid, and I don't think anyone is intended to believe otherwise.) So, depending on whether these signs were placed by someone acting on behalf of Mr. Akpata (or the Marijuana Party), or by a third party, they would seem to be in contravention of section 320 or 352 of the Act. In either case, whoever put them up would be potentially "liable on summary conviction to a fine of not more than $1,000 or to imprisonment for a term of not more than three months, or to both." [Canada Elections Act, section 500(1)]
One of the reasons for this requirement is that there are spending limits for election campaigns. If election advertising can't be traced to its source, it would be impossible to actually monitor campaign spending. So while I strongly doubt that Mr. Akpata or the Marijuana Party have the means or the intent to try to violate the spending rules, it's not a trivial matter. Other people or groups potentially do. So it's possibly a shame that this kind of creative re-use of waste materials can't be encouraged, but the law must apply equally to all.
UPDATE: I asked Mr. Akpata for comment. His response, in part, was:
i am not responsible for the signs. i did not do this, nor did i encourage nor comission any person to do this. apparently some person took it upon themselves to show support to me as a candidate. i will be forwarding this to blair longley "leader" of the marijuana party to see what if any action i should take.