Yes, Bahamut and Paladine are one and the same
A number of sections of the new D&D 5e book, Fizban's Treasury of Dragons make this explicit for the setting of Dragonlance, and thus canonical for that setting.
It's also notable, that this book is annotated explicitly with the voice of Fizban, who in previous editions has been explicitly linked as being Paladine. In the fiction of this book existing within the setting (which is something WotC has been doing with a number of their books with named authors [VGtM, MToF, XGtE, TCoE, VRGtR]), this book being written or annotated by Fizban would make this even more explicit in that context.
Where does it say this?
The two chapters of the book with the explicit references are The First World, and Dragons in Play.
The First World
This chapter discusses the origin of dragons, the role of Bahamut and Tiamat in the creation of the First World and Sardior (and subsequent creation of the different dragon families), as well as the brith of the myriad worlds of the Material Plane being
"seedling realities" formed when the First World was sundered [...]
In particular, it has specifics to say about four specific settings: Forgotten Realms, Greyhawk, Dragonlance and Eberron. For Dragonlance, part of what it has to say is making it both explicit and canonical to the setting that Bahamut is Paladine.
Dragonlance
Legends say the world of Krynn (home to the Dragonlance setting) was created in the interplay between the High God and Chaos. Its most important cosmic powers have always been the three children of the High God - Paladine, Gilean, and Takhisis, with Paladine and Takhisis easily identifiable as Bahamut and Tiamat. [...]
Dragons in Play
This chapter discusses how you would roleplay dragons, and gives you a lot of detail to help motivate them. One of the topics it discusses is the relationship of dragons to gods and religion, both in terms of the beliefs of dragons as well as various draconic beings place in religions of the multiverse.
It makes a specific distinction between the Primordial dragons (Bahamut & Tiamat) and the gods (in a metaphysical sense), but also makes it clear that they are worshipped as gods by humanoids on many worlds. One very specific example they give is the world of Krynn.
Gods and Religion
Bahamut and Tiamat, the primordial dragons and the purported creators of the First World, are the closest things to gods among dragonkind. Since they share the same fundamental connection to the Material Plane as their dragon offspring. Bahamut and Tiamat are ontologically distinct from the gods that hail from the Outer Planes. But for practical purposes they are divine [...].
[...]
On many worlds, Humanoids worship Bahamut and Tiamat as gods. On Krynn, they are the greatest among the gods, though they are known there as Paladine and Takhisis and are not always pictured as dragons. [...]
Bonus evidence
Bahamut is also Fizban on Krynn, in addition to being Paladine. This explicit link between Bahamut and Fizban is another nail in the coffin, as previous editions have made the link between Paladine and Fizban a canonical "they are one and the same". By restating this link, it makes it clear that this is an intentional link. This link appears in the Dragons in Play chapter.
Shape-shifting
[...]
Famously, Bahamut traveled the world of Krynn in the guise of a human wizard named Fizban, guiding the peoples of that world as they prepared for war against the evil forces of Tiamat. [...]
But what about planes-hopping characters?
In The First World chapter, under Dragonsight, it is made explicit that dragons are multi-world entities, through their unique feature of having
multiple incarnations of themselves across different worlds of the Material Plane.
Dragons can explicitly become aware, and potentially communicate with, or even gain control of multiple versions of those echoes, or even be regarded as gods by mortals.
Given most people's limited understanding of dragons' beliefs and philosophies, let alone dragonsight, many mortals are quick to describe dragons with dragonsight as "dragonsight". Some dragons have so successfully extended their consciousness across multiple incarnations, and so expertly coordinated their activities across multiple worlds, that they can seem godlike even to younger dragons.
This bit of lore, allows us to make even more concrete. On all worlds where there is a Bahamut, that Bahamut is actually the same being, just in a different incarnation, as the Bahamut on all of the other worlds they exist on. The same holds true for Tiamat.
So, for any planes-hopping characters who met Bahamut on one world, those characters would be known by a Bahamut they met on another world. So Fizban/Bahamut/Paladine on Krynn would know such characters that the Forgotten Realms incarnation of them has met.
