I have read the Book of Mormon and pondered it and prayed over it (just like the Bible) and have felt a confirmation of the Spirit. I have compared it to the word of God in the Bible and have had my witness of the Bible strengthened as a result. One of the stated purposes of the Book of Mormon is to convince the world of the truthfulness of the Bible (Mormon 7:9), and it has done so for me.
Intellectually, I also can accept it as canonized scripture for four primary reasons:
1) God spoke to many inside the Bible where His words are not recorded in the Bible. There literally are dozens of texts mentioned therein that are not included therein. In other words, there are multiple examples of sacred, inspired texts and revelation cited in the Bible that, if found, would be accepted (I hope) by every Christian. "Canonization" was accomplished by those who understood that they were NOT defining the totality of God's words to His children; rather, they were reviewing what records were available to them and making decisions about validity AND importance. "Canonization" has come to mean FAR more than it did originally - and I can't accept those later, artificial constraints.
2) The Biblical pattern appears clear to me: God spoke through prophets PRIOR to the birth of Jesus - including to those outside of the House of Israel (Jethro, Moses' father-in-law, is a wonderful example); He spoke THROUGH Jesus; He spoke through prophets AFTER the death of Jesus (including new visions and visitations - like Paul's); the resurrection didn't stop revelation through prophets and He never said He would stop speaking through prophets. That claim was a retroactive one made LONG after the records were first recorded - and it is EXACTLY like the claim used by the Jews to reject the New Testament after nearly 400 years of official silence after Malachi. If new records are found claiming to be God's words to ancient Polynesian prophets or Asian prophets or Icelandic prophets or African prophets - and if those records inspire people to accept Jesus as their Lord and Savior and allow Him and the Holy Ghost to bring forth good fruit unto Him and live humble lives of dedication as disciples - and in every way produce "Christians" and "good fruit of the true Vine" - then I will accept the possibility that they are, in fact, true scriptural words of God to that people. I won't accept them automatically, but I won't reject them automatically either.
3) I also have been fascinated to see what I believe are the misconceptions about the Book of Mormon (both by non-Mormons AND Mormons alike) fade away one by one as new information and evidence arises. For example, from the time I first read it so many years ago, I have thought it was a record of a very small minority of people in a very small geographic area (with the exception of the Jaredites, who appear to have been nomadic roamers of the classic Asian steppe model) - full of the same hyperbolic language that runs throughout the Bible and is a characteristic of many ancient records. I am not bothered by former beliefs of members and leaders that appear now to have been wrong, since those teachings aren't teachings OF or IN the Book of Mormon but rather beliefs ABOUT the Book of Mormon - and that is an important distinction that very few people make. (Again, it is interesting to me that so many Biblical scholars understand the nature of interpretive disagreement when it comes to Biblical scholarship but are unable to grant that same flexibility to Book of Mormon scholarship - again establishing a standard for Mormons to which other Christians aren't held.)
4) Finally, I have been struck as I have studied what the book actually says in both 1 Nephi and Ether by how incredibly different and spot-on those two books are. I don't have time or space in this post to explain that statement in detail, so I simply will leave it at that.I have heard multiple reasons why people reject the possibility that the Book of Mormon might be the word of God and a real prophetic record, but I have not heard one in all my years that is more convincing than my personal witnesses.