en.m.wikipedia.org
Difficult to say whether he belongs to Indian or Pakistani Punjab.
The halting of Iskander does seem to have occurred in Pakistani territory.
The jury is still out on Porus' precise origins it would seem.
That's the nature of history, many things are lost in time, but we do know that the major recorded battle with Alexander was fought around the river Jhelum, that's deep inside Pakistan, and after Sialkot, he went South towards Multan, and onwards to the coastline, modern day Karachi, but I might be mistaken, but he did go along the Makran coastline, so Karachi route makes sense.
Because, otherwise he would have had to go South-west from Dadu towards Lesbela and Sonmiani, and that's a difficult and water scares route, so towards Karachi or Thatta is the natural water line and from there his army travelled by foot, and boat towards Iran. And, whether origin of Porus possibly was from East Punjab is not relevant, because he was son of Punjab and nearly 3/4 Punjabis are Pakistani, Pakistan Punjab is the heart of historical Punjabi culture, so it is natural to assume he would have been from Pakistani Punjab. Even during the Sikh era, Ranjit Singh was born in Gujranwala.
It is simply a matter of how you claim your history, geography is paramount, yes, but other factors also come into play, in every shape or form. Every major Pakistani ethnic group has a majority in modern day Pakistan, and the historical centre of that group is in modern day Pakistan, with only two exceptions.
Most Pathans in this world are Pakistani, and the city with the most Pathans in the world is Karachi, but the historical centre of Pathan culture is mostly in Afghanistan. So, we still have a strong claim to that history, because the bulk of the population to which Pathan ethnic history belongs are Pakistani. The other group is Kashmiri, although Azad Kashmir has smaller population, but there is a large Kashmiri refugee population in rest of Pakistan, most from the Jammu region, so there is also a strong claim to Kashmiri history, largely on the basis of numbers. Sindh region is fully in Pakistan, and Balochistan again is the historical centre of Balochi groups and most Balochis are Pakistani.
So, for the reasons above, especially when there are gray areas, in history, the claim that Porus was ethnically linked to the soil of Pakistan is a very strong claim indeed, it is just a case of, do we want to feel shy about making that claim, or, claim him boldly as ours. Further supporting argument is that, in that period, most kingdoms were smaller in size, further reducing the possible origins of Porus to be very much Punjab centric.