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I think your question is much larger than can be answered with just three texts. Mahāyāna is not one thing, it is many Prajñāpāramitā, Madhyamaka, Pure Land, Yogacāra, Chan/Zen, Huayen etc. Similarly Vajrayāna is not one thing either.
For the Mahāyāna a comprehensive guide would have dozens of texts. At a minimum:
For Vajrayāna the situation is different. Tantras cannot be read on their own. For Shingon the two main texts are
A good introduction can be found in Kūkai: Major Works by Yoshito Hakeda. Tibetan Tantra includes many more texts, such as:
But most teaching is done through commentaries. Many of these texts cannot be understood without a commentary. Some of them require specific initiations.