Why does the Torah connect the Mitzvah of Pidyon ha'Ben with entering Eretz Cana'an?
Rashi #1 and Ramban 1 : This teaches us that the Bechoros were not sanctified until Yisrael came to Eretz Cana'an.
Rashi #2: To inform Yisrael that if they observe the Mitzvah of Pidyon ha'Ben in the desert, they will merit to enter Eretz Cana'an and continue to observe it there. 2
Ramban: Pasuk 2 taught us that Hashem sanctified the current firstborn immediately after saving them from Makas Bechoros to serve Him in whichever way He would command them. Following the Chet ha'Eigel however, He switched them for the Levi'im, ordering them to redeem the excess (See Bamidbar, 3:46). And Pasuk 15 here discusses redemption of Bechoros born after this, which will take effect only after they enter Eretz Cana'an.
Where did Hashem promise to give them (apart from the Avos) Eretz Yisrael?
Ramban #2: The Torah means that Hashem swore to their fathers that He would give it to them. 2
Above (verse 5), it says that Yisrael will enter the land of five nations. Why does it say here only Kena'ani?
Hadar Zekenim: All the [Kena'ani] nations are called on the name of their father Kena'an.