Arjuna married Chitragnda - the princess of the Manipura. Is this the same place as the current Indian state of Manipura?
Actually, it is not!
Mahabharata Adi Parva, Arjuna Vanavasa Parva Chapter 217 describes Arjuna's pilgrimage route.
Getting down from the Himalayas, he went eastward. He visited many famous pilgrimage sites in Anga (Bihar-Jharkhand) and Vanga (Bengal). For example, he went to Gaya kshetra. Then he went to Kalinga (Odisha).
From Kalinga, he went to Mahendra Parvat (Parasurama's ashrama was situated there in ancient times. It is part of the Sahyadri or Eastern Ghat mountain range).
From there, he went along the seashore and reached Manipur. So Manipur of Mahabharata was situated in Andhra or maybe in the modern-day Andhra-Odisha border. But definitely, it has no connection with the current Manipura state.
Here I am quoting the relevant verses from "A prose English translation of the Mahabharata (translated literally from the original Sanskrit text)" by Manmatha Nath Dutt, 1895, Calcutta. I have also added the link to the Mahabharata by Kisari Mohan Ganguly. Though unfortunately, in that book, verse numbers are not there.
Whatever Tirthas and other holy places were in Anga, Banga and Kalinga, he went to all of them. - Mahabharata 1.217.9
Crossing (the country of) the Kalingas and seeing on his way many countries, holy places, and charming mansions, that lord proceeded on. - Mahabharata 1.217.12
Seeing the Mahendra mountain adorned with the ascetics and going slowly along the seashores, he went to Manipur. - Mahabharata 1.217.13
To the king of Manipur, the virtuous Chitravahana, who had a beautiful daughter named Chitrangada. - Mahabharata 1.217.15