Can wireshark be set up to differentiate if a QUIC pcap is GQUIC or IETF QUIC?

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Maybe.
View->Internals->Dissector Tables then search on "quic".
GQUIC and QUIC are registered as udp Heuristics.
From the WSUG (User's Guide):

As Wireshark tries to find the right dissector for each packet (using static “routes” and heuristics “guessing”), it might choose the wrong dissector in your specific case.

Wireshark makes a SWAG and does it's best.

There are captures attached to 13881 - Add (IETF) QUIC Dissector and 15984 - gquic parser Q046 support that show each protocol dissected.