When Kanan died, he had undergone his own form of the trials.
Yoda faced his inner darkness, and at the end of season 1, Kanan realizes he has to rise above his own fear after believing Ezra had fallen to his death. He learns to overcome his fear using the Force.
In the Valley of Extinction, Yoda faces a perfect world where everyone is happy, but he rejects this world and learns to let go. Similarly, when Kanan is in the temple the second time, he is challenged with the thought that Ezra will turn to the dark side; Kanan learns to let go of the notion he can protect Ezra forever, to which the Force spirit of the Grand Inquisitor through the Force itself Knights him.
And lastly, Yoda went to Moraband (Korriban for elite ball knowers) for his final test, where the dark side itself tried to break him and seduce him with power. Kanan didn't go through something exactly like this, but when he was faced with the loss of his vision, he overcame it and learned to see not with his eyes but with the Force.
There are also a few other things that I think support the notion that he became one with the cosmic force and could partially manifest himself.
No body was confirmed to be found; you could say it was evaporated, which is fair, but his lightsaber survived the explosion in relatively good shape.
At the end of his life, the Force restored his vision one last time so that he could see Hara. This is definitely a sign he had attuned himself with the Force in some way.
Big dog... need I say more
Hera feels the presence of Kanan when on the mission to the temple of the world between worlds. You could say this is just her mourning and thinking about what Kanan would do, but he definitely has a Force spirit glow to him.
Idk if Dave confirmed it or not, but I think he is at least on the same level as Qui Gon when it comes to his ability to manifest through the Force.