Is there any reason for or significance to a tallit being used as the chuppah canopy in a Jewish wedding?
A chupa is not always a talis: other cloths are used also. But we do find that something used for one mitzva should be used for another (e.g. Nit'e Gavriel, Arbaas Haminim, chapter 61, paragraph 2), which may explain why people use a talis for a chupa. Another reason may be that it's a readily accessible large square cloth that doesn't look inappropriate.
The chupah is symbolic of the cloud that covered Mount Sinai when Hashem made a covenant with the twelve tribes of Israel. What happened that day was a marriage ceremony in which Hashem married Israel. Torah was the ketubah, the marital agreement, between Hashem and His bride.
In the years that followed this marital covenant, Hashem often accused His Bride of spiritual adultery because Israel was drawn after other gods. Eventually, Hashem divorced the northern ten tribes (Israel) because of this (see Hosea chapter 1). Though He severely disciplined Judah, He spared them from divorce.
Therefore, a Hebrew wedding ceremony is symbolic of the ultimate, eternal marriage of Hashem with His people Israel.
Part of the reason a tallit is often used as a covering is the fringes, the tsitsis. In Numbers 15 Hashem tells Israel to make "fringes" on the edges of their garments. These fringes symbolize the edges of the cloud of glory over Mount Sinai and they way the light of Hashem would flash through. Psalm 119 equates Torah of Moses with light. This implies that the flashing beams of sunlight coming through the fringes are the light of Hashem that comes into our lives as we obey Him and keep His Torah. Numbers 15:39 say that these fringes are to remind the Israelites of their marriage covenant that we call Torah. Therefore, the tallit and its fringes remind the couple that they are part of a greater, eternal covenant and that they should keep Torah from their hearts all the days of their lives.